This invention relates to improvements in a method of changing a rolling schedule while a work strip is passing through a tandem rolling mill without stopping the mill.
In conventional methods of changing the rolling schedule during the rolling of the work strip having a gauge change point in multi-stand tandem rolling mills, the screw-down position of the roll on the first roll stand has been updated when the gauge change point arrives at that roll and this process has been repeated with the succeeding roll stands while the well-known constant volume principle of material mass flow is fulfilled so that it has been attempted to prevent a change in tension of the work strip and others. In order to prevent a change in strip tension and others, Japanese patent publication No. 17145/73, for example, discloses that the ratio of rolling speed between adjacent roll stands is changed from its value according to the original schedule of operation to a new value at each roll stand at the same time point. However, the conventional roll speed control, as described above, has paid no attention to a decrease in an overall change in the roll speed which occurs in tandem rolling mills. Therefore, errors in the calculation of the rolling schedules, errors developed in an associated mill speed control system, etc., have caused, in actual operation, external disturbances which are, in turn, attended with transient disturbances occurring in the mass flow upon a change in the rolling schedule, such flow following the constant volume principle of material mass flow. Those transient disturbances can not be suppressed. For example, the interstand tension might be excessive and the roll force might be concentrated on a specified roll stand. This has resulted in the disadvantage that, in order to attain stable operation, the rolling schedule must be changed at a sacrifice in the rolling efficiency, that is, at reduced roll speeds.
Accordingly, it is an object of the present invention to provide a new and improved method of changing a rolling schedule during the rolling of a work strip in a tandem rolling mill without stopping the mill; such a method can minimize transient disturbances due to errors in the calculation of rolling schedules, errors in correction of the screw-down position and the roll speed, etc.
It is another object of the present invention to provide a method of changing a rolling schedule during the rolling of a work strip in a tandem rolling mill enabling an improved stability of operation and improved rolling efficiency, in addition to the minimization of the transient disturbances of the mass flow, as described above.